Inverse jet electrochemical machining for functional edge shaping of micro bores

Micro bores are used for several high-precision applications, especially in hydraulic systems and fuel injectors. In this case the shape, particularly the edge rounding of the injection spray hole, has a significant influence on the atomization of fluids and therefore also on the combustion process [1]. From the present knowledge about the relationship between bore geometry and hydraulic properties requirements were derived which are not feasible applying conventional manufacturing techniques. In particular, it is currently not possible to adjust the flow coefficient and the cavitation point independent of each other. The flow coefficient significantly influences the atomization, while the cavitation is necessary to prevent coking of the injection holes. One way to decouple the flow coefficient and cavitation behavior is a functional edge rounding of the borehole. This cannot be represented by the previous ly applied hydroerosive rounding. Therefore inverse Jet Electrochemical Machining (inverse Jet-ECM) opens up new possibilities, as the erosion area is localised by the jet. In Jet-ECM the electrolyte is supplied through a nozzle at an average speed of about 20 m/s and adjusted perpendicular to the work piece surface. Forming a free jet leads to a high localization of the current density resulting in a much localized machining area direct below the nozzle [2]. In this study an edge rounding of the micro nozzle bore is realized by an inversion of the Jet-ECM principle.